It's a small extension, so the FAQ is small.
Installing the extension
Install Structly from the App Store, then enable the Safari extension in Settings → Safari → Extensions → Structly. On macOS, the same toggle lives under Safari → Settings → Extensions.
Sync between devices
Nothing to set up. Preferences sync over iCloud automatically when you're signed into the same Apple ID.
Safari updated and the extension stopped working
Usually a permissions reset. Open Safari, Manage Extensions, toggle Structly off and back on, and re-enable "Allow on Every Website" if you had it. If it's still off, restart Safari once.
The extension didn't format a page
Structly only triggers on responses Safari recognises as JSON (Content-Type: application/json). Pages that send JSON with text/html or text/plain headers won't trigger automatically. Reload with the URL bar focused and Structly should pick it up on the second pass.
Bug, feature request, or hello
Email me at hechen.dream@gmail.com. Real reply, usually within a day.